With the spread of mobile terminals such as smartphones the traffic between a base station that couples a mobile terminal to a wireless communication network and an exchange office is increasing. It is examined to dispose a base band unit (BBU) in an exchange, office and dispose a remote radio head (RRH) in each base station such that the traffic of a mobile front hall of the RRHs is accommodated on a passive optical network (PON) having a large transmission capacity. The BBU and each RRH are coupled to each other through an optical line termination (OLT) and an optical network unit (ONU) in the PON.
As the PON applied to the mobile front hall, for example, there is “next generation (NG)-PON2” that uses wavelength division multiplexing (WDM). It is to be noted that “NG-PON2” is prescribed in international telecommunication union telecommunication standardization sector (ITU-T) Recommendation G.989 series.
Examples of the related art include Japanese Laid-open Patent Publication No. 2014-165614 and Japanese Laid-open Patent Publication No. 2014-110574.
The RRH is disposed in a small cell base station having a cover area smaller than that of an ordinary base station, and a large number of small cell base stations are provided in an ordinary macro cell to increase the transmission capacity of the mobile front hall. However, if all small cell base stations operate, there is the possibility that the power consumption may become excessive, and therefore, small cell base stations whose traffic is low are controlled so as to be placed into a sleep state in which the power consumption is low.
On the other hand since a great bandwidth is required for a small cell base station having high traffic, to the ONU coupled to the RRH of the small cell base station, a channel of point-to-point (PtP) WDM prescribed as a function of “NG-PON2” is allocated upon activation from the OLT. Consequently, since the OLT and the ONU communicate one to one, the RRH may communicate with the BBU occupying the bandwidth of the channel.
However, in the case where a plurality of ONUs remain in a non-activated state in the PON, the OLT activates only the ONU from which a registration request is received earliest, and therefore, it sometimes activate an ONU other than the ONU coupled to the RRH of the communication destination of the BBU. In this case, the ONU coupled to the RRH of the communication destination remains un-activated, and no link is established between the ONU and the OLT. Accordingly, since the BBU fails to communicate with the RRH, there is the possibility that hindrance in provision of a communication service may be caused.
Taking the foregoing into consideration, it is desirable to provide a transmission device, an optical termination device, a transmission system, and a transmission method that make communication between a BBU and an RRH corresponding to each other possible.